If Wigan Athletic find the steel to overcome Manchester City in the FA Cup final their victory will have been made from girders. “We have a great Scottish contingent at the club so the Irn-Bru is going to be flowing,” Roberto Martínez, Wigan’s manager, said.

Three of Martínez’s players – Gary Caldwell, James McArthur and Shaun Maloney – are Scots while a fourth, Republic of Ireland international James McCarthy, was born in Glasgow.

Martínez has banned all alcohol until Wigan have negotiated this crucial period of Cup final and two Premier League games.

“The players are conscientious enough to wait eight days and then we can have the celebration of our lives but Irn-Bru is not banned at all,” Martínez said.

“My first FA Cup game was Runcorn away in 1995 [as a Wigan player] and we went in a bus. It was full of alcohol. It was an eye-opener. It used to be a case of train hard and party hard. But you can’t do that any more.

"They wouldn’t be swigging from bottles of champagne now because if you have something in your body you would be sweating after 10 minutes on the pitch and can’t even move.”

Martínez was sitting in Haigh Hall, the old home of the Earls of Crawford and Balcarres. The Spaniard was sipping coffee from a bone china cup and looking at a lapel badge presented to him by Wigan Council that said “BELIEVE”.

He knows what an upset it would be if Wigan beat City. “It’s one of those games where everyone loves an underdog. When I go to World Cups or European Championships, when you have no attachment to any of the two nations you always want the underdog to win. Even Spain were the underdogs once!

“Anyone who knows the FA Cup knows there are incredible upsets. But the major upsets came in the late ’70s and ’80s. I think Coventry [’87 v Spurs] and Wimbledon [’88 v Liverpool] were the last two. It shows you the game has become more demanding. It’s hard to have an upset.

"City are a team that like to control games with possession and on a pitch like Wembley it is very difficult to upset their rhythm. You have seen the story of Bradford in the League Cup: they upset everyone but then they get into the final and on a big pitch, against a team that controls the ball [Swansea City], and it becomes very difficult. We need to play like a big team and we are capable of doing that.”

Famously polite, Martínez mulled over a question of whether he was hard enough to be a top manager. Could he be tough with his players?

“You need to deal with human beings from Monday to Friday and footballers on Saturday. That honest streak that you’re looking for needs to come out on match-days. I lose my temper quite easily if people drop their standards.”

He was certainly hard on the Football Association for the ­timing of the Cup final. “This is not the right time. Traditionally the FA Cup final has always been the last game of the season and it makes sense. City are going into the final just fighting for the final. We are going to the final in the middle of our key moment of the season. This is supposed to be one of the biggest games in world football and the timing could devalue the competition.”

Martínez then smiled at the mention of his chairman, Dave Whelan, refusing to wear a club suit when he leads the team out. “He’s going to keep his old one. We tried [to get him to change]. He said: 'No, this suit is still in good condition’.” Martínez does not believe in lucky charms. “No. I was born on Friday the 13th so I don’t have superstitions!”